The present invention relates to a valve operating apparatus for an internal combustion engine. More particularly, the invention involves valve operating apparatus capable of changing the modes of operation of both the intake valves and the exhaust valves associated with the cylinder of an internal combustion engine according to varying operating conditions of the engine.
Japanese Laid-Open Patent Publication Nos. 59-226216 and 61-19911 are directed to valve operating mechanisms of the described type. These mechanisms are designed such that the intake valves and the exhaust valves have substantially the same operating modes. Since exhaust gas emitted from an engine has a high temperature and flows at a high velocity, it is desirable that, under certain conditions, the exhaust valve have a cross-sectional area of valve opening which is smaller than that of the intake valve. Where the above prior art valve operating mechanisms are designed to operate the intake and exhaust valves in accordance with substantially the same operation modes it is impossible to operate the respective valves to accommodate changing the exhaust valve opening appropriately under these certain conditions.
It is to the amelioration of this problem, therefore, that the present invention is directed.